Gas turbine engines generally include a compressor, a combustor, and a turbine arranged in serial flow combination. Air enters the engine and is pressurized in the compressor. The pressurized air is then mixed with fuel in the combustor. Hot combustion gases are generated when the mixture of pressurized air and fuel are subsequently burned in the combustor. The hot combustion gases flow downstream to the turbine, which extracts energy from the combustion gases to drive the compressor.
The pressurized air exiting the compressor is discharged at a relatively high velocity. Before flowing downstream to the combustor, the pressurized air typically passes through the pre-diffuser of an inner diffuser case upon exiting the compressor to decrease the velocity of the pressurized air and minimize pressure losses. Additionally, in some conventional engines, the pre-diffuser also directs a secondary airflow through a different flow path to separate it from intersecting with the pressurized air. In particular, the separate flow paths of the secondary air and the pressurized air may be achieved by disposing the inner diffuser cone aft of the thrust balance strut hole located in each of the plurality of struts of the pre-diffuser. The thrust balance strut hole in each strut may direct the secondary airflow flowing from a bearing compartment into a high pressure compressor bleed cavity. In some common inner diffuser cases, for example, the inner diffuser cone may be aligned axially with the inner diffuser skirt and the pre-diffuser outlet. While generally effective at separating the airflows, the different pressures and velocities of the various airflows may cause high stresses on the inner diffuser case due, in part, to the axial location and relative positioning of the inner diffuser case cone to the inner diffuser case skirt and the pre-diffuser outlet. Accordingly, there is a need for an inner diffuser case that incurs less stress when separating the pressurized air from intersecting with the secondary airflow.